This invention relates to "phantom" lamps and more particularly to such lamps which incorporate safety devices.
Conventional fluorescent lamps generally operate in series circuit connected pairs utilizing a single ballast transformer. Lamps and ballast transformer systems of the so-called rapid start or pre-heat (two-pin) type in which the filaments of a fluorescent lamp are heated, and of the so-called instant start (one-pin) type, in which no filament is provided, are well known.
In response to the energy crisis which began in the early 1970's, attempts were made to conserve energy. In this regard, it was frequently desired to remove one of the lamps from a two lamp fixture leaving the remaining lamp to provide illumination. This end, however, could not be easily accomplished since the two lamps were connected in series and the removal of one lamp prevented the operation of the other. To overcome this problem, two embodiments of a device, commonly referred to as a "phantom" lamp (so-called because the "phantom" lamp is frequently configured to have the same general appearance as a conventional fluorescent lamp), have been provided. In one embodiment, the phantom lamp is merely a conductor which is connected between the two sockets of the fixture which have been vacated by the removal of a lamp. The connection of the conductor between the two sockets completes the circuit, thereby permitting the remaining lamp to operate. In the other type of phantom lamp, the two sockets of the fixture which were intended to receive the removed lamp are connected to one another by a capacitor. Such a phantom lamp is described in U.S. Pat. No. 3,956,665. The type of phantom lamp taught by the noted patent is superior to that of the embodiment in which a mere conductor is provided because the capacitor serves to limit the current in the lamp circuit and to aid in the correction of power factor problems which arise from the removal of one of the fluorescent lamps from the circuit. It will be understood, of course, that neither of the foregoing devices referred to as phantom lamps are truly lamps, since they provide no illumination. They are, as previously stated, either mere conducting wire or a capacitor of appropriately selected capacitance. The devices are, however, customarily enclosed in non-evacuated glass tubes of a size generally equal to that of the fluorescent lamps which they are to replace. The tubes further are provided with capped ends and either one or two pin connectors as appropriate, in the same manner as the fluorescent lamps for which the phantoms are the intended substitutes.
The phantom lamps described above, however, both suffer from a major disadvantage with regard to safety. The danger arises from the possibility that when one end of the phantom lamp is inserted into one socket of a two socket pair, the person inserting the phantom lamp will touch the opposite end of the lamp while such individual is at electrical ground. In such event, a substantial electrical current can flow through the individual causing serious injury or even death.